A pH sensor with automatic water storage and replenishment, including a substrate, a working electrode, a reference electrode, a first piezoelectric micropump, a water storage device, and a second piezoelectric micropump. The working electrode, the reference electrode, the first piezoelectric micropump, the water storage device, and the second piezoelectric micropump are arranged on the substrate. The working electrode and the reference electrode are each connected to a bonding pad through an electrode lead. The second piezoelectric micropump, the water storage device, and the first piezoelectric micropump are sequentially communicated, and a liquid flows to the working electrode via an outlet of the first piezoelectric micropump.